Solubility measurements are to be made on Ca8H2(PO4)6.5H2O in the system Ca(OH)2-H3PO4-H2O; carbonate apatites, CaHPO4.2H2O and Ca5(PO4)3OH in the system Ca(OH)2-H3PO4-H2O-CO2; tooth and bone mineral in vitro; enamel in vivo; beta-Ca3(PO4)2 in the system Ca(OH)2-H3PO4-H2O-Mg(OH)2, and of the various calcium phosphates in buffer solutions. Microcalorimeter measurements will be made on the reactions of F- and various cations with hydroxyapatite surfaces. The role of Galvani potentials in various dentally related phenomenon will be investigated. Laboratory, animal, and clinical studies will be carried out on procedures for remineralizing incipient caries and for dissolving dental calculus. Crystal structures of various dentally related compounds and of non-stoichiometric and impure apatites will be determined from x-ray and neutron diffraction data, and interlayering between Ca5(PO4)3OH and Ca8H2(PO4)6.5H2 will be studied by computer methods.